The present invention relates generally to stretch bend apparatus for forming hollow workpieces and particularly to a snake tool device for supporting a wall or walls of a hollow extrusion having a non-symmetrical shape in cross section while the extrusion undergoes stretching, bending, and twisting.
Elongated hollow members can take many shapes in cross section. This is particularly true for hollow aluminum extrusions employed in constructing spaceframes for motor vehicle, for example, as shown in U.S. Pat. No. 4,618,163 to Hasler et al. Such extrusions are bent and stretched to provide lineals having appropriate shapes for forming a vehicle frame, as a frame cannot generally be constructed with straight pieces only. The underlying principle of stretch forming involves applying tension to a generally straight workpiece such that it yields plastically, and deformation is imposed by bending or wrapping the workpiece around the curved surface of a die that results in proper modes of plastic flow so that the workpiece retains the desired linear configuration after stretching and bending, and after being subjected to certain twisting, depending upon the use of the formed workpiece. Stretch bend apparatus includes two, opposed clamping assemblies that grip the ends of an elongated workpiece to bend the same around the curved surface of a die while clamping assemblies apply tension to the workpiece. The surface of the rounded die is generally configured to that of the cross sectional shape of the workpiece so that the workpiece is properly supported while it is being formed. If the workpiece is hollow, the walls of the workpiece can be supported against collapse by a pressurized fluid supplied to the interior of the workpiece. Though the walls of a hollow, non-symmetric extrusion can be supported internally by a pressurized medium, certain wall portions of such a hollow extrusion will tend to bulge outwardly in the proces of the extrusion being formed over the curved die surface. The walls or wall portions of the hollow extrusion seated in and against the die surfaces are, of course, supported by the die surfaces.